Put Geo node statuses in the database

Description

For Geo we need the status of the different nodes in several places. So instead of fetching the status every time, have a worker to fetch it regularly and store it in the database. Other code can then get it from the database instead of fetching it themselves.

Proposal

• Add worker that fetches Geo node statuses on a regular basis (e.g. every minute)
• Remove all other uses of Geo::NodeStatusService, but get the node statuses from the database
• Make /admin/geo_nodes properly work with the mechanism

Links / references

Follow-up to a discussion started by @nick.thomas (and also this one):

I don't like that we're going to have multiple unrelated jobs polling this endpoint for subsets of the data (this MR, https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3172/diffs#7d8625b2d782cbaf784b00c0f7fe9bb8ddfdb968_0_12 from @to1ne, the existing status page, and then there's the API endpoint to consider as well).

WDYT to - probably in a follow-up MR - adding a geo_node_statuses table that the primary updates by cronjob every minute? All uses of GeoNodeStatus would use the database rather than HTTP calls.